Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

An example capacitive switch apparatus comprises a capacitive switch
sensor providing a capacitive switch signal, a capacitive reference
sensor providing a capacitive reference signal, and an electronic
circuit, receiving the switch and reference signals and detecting switch
activation by comparing the switch signal level with a threshold level.
The threshold level is adjusted as a function of the reference signal
level. The reference signal is obtained, for example during periods of
operator proximity to the reference sensor. For a finger-operated switch,
the reference signal is obtained when a finger is proximate the reference
sensor.

Claims:

1. An apparatus, the apparatus being a capacitive switch comprising: a
capacitive switch sensor, providing a capacitive switch signal; a
capacitive reference sensor, providing a capacitive reference signal; and
an electronic circuit, receiving the capacitive switch signal and the
capacitive reference signal, the electronic circuit detecting switch
activation by comparing the capacitive switch signal to a threshold
signal level, the threshold signal level being adjusted as a function of
the capacitive reference signal.

2. The apparatus of claim 1, the apparatus comprising a plurality of
capacitive switch sensors, the threshold signal level for each capacitive
switch sensor being adjusted as a function of the capacitive reference
signal.

3. The apparatus of claim 1, the capacitive switch being manually
activated, the capacitive reference sensor providing the capacitive
reference signal during periods of manual proximity to the capacitive
reference sensor.

4. The apparatus of claim 3, the apparatus being a capacitive switch
apparatus for a vehicle, the capacitive switch being manually activated
by a vehicle operator.

5. The apparatus of claim 4, the capacitive reference sensor being
located within a vehicle steering control.

6. The apparatus of claim 5, the vehicle steering control being a
steering wheel.

7. The apparatus of claim 4, the capacitive reference sensor being
located within a control component associated with the vehicle.

8. The apparatus of claim 7, the control component being a climate
control adjuster or an entertainment device controller.

9. The apparatus of claim 4, the capacitive reference sensor being
located in a door-handle or armrest of the vehicle.

10. The apparatus of claim 4, the capacitive reference sensor being
associated with an ignition key for the vehicle.

11. The apparatus of claim 4, the electronic circuit including a
microprocessor, the threshold signal level being adjusted using software
executed by the microprocessor.

12. A capacitive switch apparatus for a vehicle, comprising: a capacitive
switch sensor, operable to provide a capacitive switch signal; a
capacitive reference sensor, operable to provide a capacitive reference
signal; and an electronic circuit, receiving the capacitive switch signal
and the capacitive reference signal, the electronic circuit detecting
switch activation by comparing the capacitive switch signal with a
threshold signal level, the threshold signal level being adjusted as a
function of a signal level of the capacitive reference signal, the
capacitive reference signal being obtained during periods of vehicle
operator hand proximity to the capacitive reference sensor.

13. The apparatus of claim 12, the capacitive reference signal being
obtained at intervals during vehicle operation, the threshold level being
further adjusted as a function of changes in the capacitive reference
signal.

14. The apparatus of claim 12, the vehicle having a steering wheel, the
capacitive reference sensor being located within the steering wheel.

15. The apparatus of claim 12, the capacitive reference sensor being
located on or within a control component associated with the vehicle.

16. The apparatus of claim 15, the control component being selected from
the group consisting of a steering wheel, a climate control, an
entertainment device control, a seat adjustment, and an ignition key.

17. A method of detecting an activation of a capacitive switch within a
vehicle, the vehicle having a vehicle operator, the method comprising:
obtaining a reference signal from a capacitive reference sensor when a
hand of the vehicle operator is proximate the capacitive reference
sensor; using the reference signal to determine a threshold level for
switch activation; obtaining a capacitive switch signal from a capacitive
switch sensor; comparing the capacitive switch signal with the threshold
level to detect activation of the capacitive switch.

18. The method of claim 17, the capacitive reference sensor being located
so that starting and operating the vehicle brings the hand of the vehicle
operator proximate the capacitive reference sensor.

Description:

FIELD OF THE INVENTION

[0001] The invention relates to electrical switches, in particular to
capacitive switches.

BACKGROUND OF THE INVENTION

[0002] Capacitive switches can replace mechanical switches in a variety of
applications. However, conventional capacitive switches are prone to a
variety of problems, such as nonresponsiveness, false triggering, and
electrical noise.

SUMMARY OF THE INVENTION

[0003] Examples of the present invention include apparatus and methods
related to an improved capacitive switch.

[0004] An example apparatus comprises a switch sensor, a reference sensor,
and an electronic circuit receiving a sensor signal from the switch
sensor and a reference signal from the reference sensor. The electronic
circuit detects switch operation when the sensor signal crosses a
threshold signal level. The threshold signal level is adjusted as a
function of the reference signal, allowing improved operation of the
capacitive switch. The electronic circuit used to adjust the threshold
signal level may be a hardware circuit, or a microprocessor based circuit
that adjusts the threshold via software. Examples below relate to a
capacitive switch sensor and a capacitive reference sensor, but analogous
approaches can be used with other switch technologies.

[0005] For example, in the case of a finger-operated capacitive switch,
both the reference signal level and switch sensor level (in each case,
when a finger is close) are correlated with certain physical properties
of the finger. These properties include skin electrical conductivity,
finger dimensions, the presence of a glove or other covering, and the
like. Hence, by adjusting the threshold signal level as a function of the
capacitive reference signal, improved operation of the capacitive switch
can be obtained. The effects of the aforementioned finger physical
properties on switch operation can be appreciably reduced.

[0006] In some examples, the threshold signal levels for a plurality of
capacitive switch sensors may be adjusted as a function of one or more
capacitive reference signals.

[0007] The capacitive reference signal is obtained from a capacitive
reference sensor during periods of manual proximity to the capacitive
reference sensor, or the presence of some other configuration similar to
that used for switch operation.

[0008] Examples of the present invention include an improved capacitive
switch apparatus for a vehicle. A capacitive reference sensor may be
located within a vehicle steering control (such as a steering wheel),
other control component associated with the vehicle (such as a power or
adjustment control for a climate control apparatus, entertainment device,
and the like), or a location likely to be touched by a vehicle operator
in the process of entering and/or starting vehicle operation (such as an
exterior or interior door-handle, armrest, seat adjustment control, or
ignition key for the vehicle). The capacitive reference sensor may be
located so that starting and operating the vehicle brings the hand of the
vehicle operator proximate one or more capacitive reference sensors
during typical operation.

[0009] The electronic circuit determines switch activation by comparing
the capacitive switch signal with a threshold signal level, where the
threshold signal level is adjusted as a function of a signal level of the
capacitive reference signal.

[0010] The electronic circuit may be an analog or digital circuit, and in
some examples may include a microprocessor. Software may be used to
calculate an adjusted threshold signal level based on the reference
signal levels obtained. Software and/or other circuitry can be further be
used to determine when the reference sensor is providing a reference
signal.

[0011] The capacitive reference signal may be obtained at intervals during
vehicle operation, and the threshold level may be further adjusted as a
function of changes in the capacitive reference signal. For example, a
vehicle operator may remove a glove as the vehicle warms up, and this may
be reflected in a changed level of reference signal.

[0012] The threshold level may be set to a predetermined value until a
suitable reference level is obtained, which may, for example, be the
previous threshold level used or an average of previous threshold levels.

[0013] An example method of detecting an activation of a capacitive switch
(for example, within a vehicle) comprises obtaining a reference signal
from a capacitive reference sensor when a hand of an operator is
proximate the capacitive reference sensor, using the reference signal to
determine a threshold level for switch activation, obtaining a capacitive
switch signal from a capacitive switch sensor, and comparing the
capacitive switch signal with the threshold level to detect activation of
the capacitive switch.

[0014] In examples of the present invention, the threshold level for
switch activation is adjusted as a function of a reference sensor signal.
For example, if the reference signal changes by a reference value when an
operator touches the reference sensor, the threshold value for one or
more switch sensors can be adjusted as a function of the reference value.
In some examples, the threshold value, as measured from an appropriate
baseline, may be approximately or substantially equal to the reference
value.

[0015] The threshold tolerance may be maintained at a constant absolute
value as the threshold is adjusted. Alternatively, the tolerance may be a
predetermined proportion of the threshold value, or otherwise related
value.

[0024] A conventional capacitive switch may comprise a capacitive switch
sensor providing a sensor signal and an electronic circuit receiving the
sensor signal. The electronic circuit uses a predetermined threshold to
determine when the sensor signal corresponds to an "activated" state

[0025] However, the sensor response depends on a number of factors, such
as the size, conductivity, and physical state of e.g. a finger used to
operate the switch. For example, a gloved hand may give a much smaller
change in sensor signal, if a gloved finger is used to activate the
switch.

[0026] The threshold used may have a tolerance, and broadening the
tolerance allows smaller changes in the sensor signal to be registered as
switch activation. However, this also makes the switch more sensitive to
false operation, or misdetection of switch activation.

[0027] Hence, the optimum threshold level may vary considerably according
to electrical parameters an operator's hand, such as skin conductivity,
finger size, or the presence of dielectric or conducting elements on the
hand of the operator (e.g. the presence of gloves, rings, and the like).

[0028] In examples of the present invention, the threshold level is
adjusted as a function of the capacitive reference signal, so as to
obtain a threshold level that is closer to an optimized level for the
capacitive switch. Examples of the present invention allow adjustment of
threshold levels to allow improved performance of a capacitive switch.

[0029] An example capacitive switch apparatus comprises a capacitive
switch sensor providing a capacitive switch signal, a capacitive
reference sensor providing a capacitive reference signal, and an
electronic circuit, receiving the capacitive switch signal and the
capacitive reference signal. The electronic circuit detects switch
activation by comparing the switch signal with a threshold level. The
electronic circuit used to adjust the threshold level(s) may be a
hardware circuit, or a microprocessor based circuit that adjusts the
threshold via software.

[0030] An apparatus may include one or more capacitive switch sensors and
one or more capacitive reference sensors. The threshold level for each
switch may be adjusted as a function of the capacitive reference
signal(s).

[0031] In examples below, a reference sensor generally refers to a
capacitive reference sensor, and a switch sensor refers to a capacitive
switch sensor. The electronic circuit uses the reference signal to adjust
the operational range over which the sensor signal corresponds to the
activated state, and may be a micro-processor based circuit that adjusts
the thresholds using an algorithm responsive to reference signal levels.

[0032] A capacitive switch may be finger-activated, and generally the
capacitive switch signal increases as a response to increased sensor
capacitance as the finger of the operator approaches the capacitive
switch sensor. The capacitive reference sensor is used to obtain a
capacitive reference signal when the finger of the operator is proximate
the capacitive reference sensor. Finger proximity to the reference sensor
may be determined by various methods. For example, if the reference
sensor is located within a controller for vehicle heating and/or air
conditioning, the reference signal may be determined as the controller is
operated. A controller may be a dial or knob including a reference
sensor, and in some examples may be a capacitive slide switch. In the
latter example, capacitive slide switch sensors may be used to provide
the reference signal.

[0033] The capacitive reference signal may be determined each time a hand
(e.g. a finger) of the operator is proximate the capacitive reference
sensor. The threshold may be appropriately adjusted each time a new
reference signal is obtained, for example as a rolling average.

[0034] In some examples, a capacitive switch apparatus is used within a
vehicle, for example to control operation of the vehicle (including
accessories therein). The capacitive switch can be manually activated by
a vehicle operator, for example by touching with a finger.

[0035] An example capacitive switch apparatus for a vehicle comprises a
capacitive switch sensor operable to provide a capacitive switch signal,
a capacitive reference sensor operable to provide a capacitive reference
signal, and an electronic circuit, receiving the capacitive switch signal
and the capacitive reference signal. The electronic circuit detects
switch activation by comparing switch and threshold levels, for example
activation being indicated when the switch signal level crosses a
threshold level. The threshold level is adjusted as a function of the
capacitive reference signal level. The electronic circuit used for
adjusting the threshold(s) may include a microprocessor, and used to
adjust the thresholds using software. For example, a software algorithm
can be used to determine an adjusted threshold level using reference
sensor signals.

[0036] The capacitive reference signal may be obtained during periods of
vehicle operator hand proximity to the capacitive reference sensor. The
capacitive reference signal level is used to adjust the threshold level,
and may be an average level of some or all of the reference signal
obtained. For example, the reference signal used to adjust the threshold
level may be a signal level average, and may optionally exclude signal
portions near the beginning and/or end of the collected signal.

[0037] The capacitive reference sensor can be located within a vehicle
steering control, such as a steering wheel (in the case of an
automobile), yoke, helm, joystick, and the like. The capacitive reference
sensor may be located within a control component associated with the
vehicle (such as a climate control adjuster or an entertainment device
controller), a door-handle or armrest of the vehicle, ignition key, or
other location.

[0038] In some examples, the reference signal may be provided by a
portable electronic device, used by the vehicle operator, including one
or more capacitive sensors. For example, a portable electronic device may
become in electronic communication with the vehicle as the operator
enters the vehicle, or soon after, allowing an appropriate reference
signal to be provided.

[0039] The capacitive reference signal may be obtained at intervals during
vehicle operation, for example each time the vehicle operator touches a
component including a reference sensor. The threshold level may be
further adjusted as a function of changes in the capacitive reference
signal, for example as a rolling average.

[0040] A method of detecting an activation of a capacitive switch includes
obtaining a reference signal from a capacitive reference sensor when a
hand of the operator is proximate the capacitive reference sensor, using
the reference signal to determine a threshold level for switch
activation, obtaining a capacitive switch signal from a capacitive switch
sensor, and comparing the capacitive switch signal with the threshold
level to detect activation of the capacitive switch. For vehicular
implementation, the capacitive reference sensor can be located so that a
normal starting process, and/or operating process for the vehicle brings
the hand of the vehicle operator proximate the capacitive reference
sensor.

[0041] A capacitive sensor provides a sensor signal that is responsive to
the proximity of a dielectric or conducting object. Any appropriate
design of capacitive sensor can be used in capacitive switches, for
example sensors including two or more conducting elements separated by a
dielectric gap. As a person's finger approaches the sensor, the
capacitance signal of the sensor may increase above threshold level (or
otherwise be compared with the threshold level) allowing detection of
switch activation.

[0042] Capacitive switches according to examples of the present invention
can be used to replace conventional electrical switches, e.g. in
automotive environments, and examples of the present invention include
apparatus including such switches.

[0043] FIG. 1A illustrates a conventional switch operation. The figure
shows capacitance value as a function of time. The peak in curve 10
corresponds to a finger approaching the sensor. In this example, the
switch operates correctly, as the capacitance values goes above a
threshold value.

[0044] FIG. 1B shows mis-operation of the capacitive switch. In this case,
the capacitance value 10 fails to reach the threshold value for switch
operation. The problem shown in FIG. 1B may arise from various factors,
such as a gloved hand, dry hand, particularly small finger, and the like.

[0045] FIG. 1C illustrates a simple but possibly unsatisfactory solution,
which is to increase the threshold tolerance, effectively lowering the
threshold level for switch operation. However, this increases the risk of
inadvertent switch operation or erroneous operation due to electrical
noise. If the threshold for switch operation is low enough to account for
any source of reduced sensitivity, then overall performance will be
compromised.

[0046] FIGS. 2A-2B illustrate an improved approach using a capacitive
reference sensor. The reference sensor may be a similar design to the
switch sensor, and is used to provide a reference signal when the
operator places a finger on or proximate the reference sensor.

[0047] FIG. 2A shows a reference signal 20. The sensor threshold is then
adjusted as a function of the reference signal. In examples of the
present invention, the recommended finger threshold, and hence the
effective threshold level for switch activation, can be determined from
the reference signal. For example, an average value of the reference
signal may be determined and used as the threshold level for switch
activation.

[0048] FIG. 2B shows the original finger threshold of a capacitive switch,
and an adjusted or recommended finger threshold determined from the
reference sensor as shown in FIG. 2A. The thresholds are shown as dashed
lines that also indicate the ±tolerance levels. The sensor signal
shown in FIG. 2B is sufficient for switch activation, as the sensor
signal crosses the recommended threshold level within the shaded region.
However, the same sensor signal would not activate the switch using the
original finger threshold. This illustrates how adjusting the threshold
level using the reference signal improves switch operation.

[0049] The tolerance, as illustrated in FIGS. 1A-1C, need not be changed.
FIG. 1C shows the recommended finger threshold level unchanged, but the
tolerance on the threshold level increased so that effectively the
threshold for switch operation is lower.

[0050] The threshold for switch activation equal to the recommended finger
threshold minus the tolerance is hence adjusted according to the
determined reference signal.

[0051] For automotive applications, the reference sensor can be located so
that an operator touches the reference sensor in normal course of vehicle
operation. For example, a reference sensor may be located in the steering
wheel. A plurality of reference sensors may be located in the steering
wheel to increase the chance of one being touched.

[0052] In other examples, the reference sensor may be located in a control
component within the vehicle, such as the on/off switch, volume control,
or other controller of a radio or other in-car entertainment device, a
climate control component, headlight control or other electrical switch,
or similar location.

[0053] In some examples, the reference sensor may be associated with a
vehicle key used to open or turn on the vehicle. For example, the unlock
button or other portion of an electronic vehicle key may include a
capacitive reference sensor. The reference signal level may be
communicated electrically or wirelessly to the electronic circuit that
determines the threshold level for a switch sensor.

[0054] A reference sensor may be located e.g. in any conventional
electrical switch, for example in a button, or within any surface
contacted by the operator's finger(s). For example, a reference sensor
may be located within a power switch or other portion of an apparatus,
and used to adjust threshold levels associated with capacitive switches
used in the same apparatus, or any other apparatus.

[0055]FIG. 3 shows possible locations for a reference sensor, such as
within the steering wheel 50, radio button 52, key 54, turn signal or
other stalk control 56, gearshift knob or other transmission controller
58, climate controller 60, emergency brake handle 62, or door handle 64.
Other examples include seat position controllers, exterior door handles,
armrests, and the like.

[0056] FIG. 4 shows a simplified schematic of an example improved
capacitive switch apparatus. The apparatus comprises reference sensor 60
and switch sensors 62 and 64. There may be a plurality of switches having
the threshold adjusted by a single reference signal. The electronic
circuit (control circuit 66) receives the reference signal and the switch
sensor signals. In some examples, a plurality of reference sensors may be
used and the reference signal determined from one or more of these
reference signals.

[0057] The control circuit 66 determines the threshold level using
reference measurement circuit 68. Collection of the reference signal may
be triggered by an electrical signal provided by the component with which
the reference sensor is associated. The reference measurement circuit
provides a reference signal level (for example an average value of the
reference signal collected over a period of time) to threshold control
circuits 70 and 72 associated with switch sensors 62 and 64,
respectively. The threshold control circuits use the reference signal, in
particular the signal level thereof, to adjust the threshold level used
to determine switch activation.

[0058] The control circuit 66 has switch outputs shown at 74 and 76.
Switch output 74 is a signal that goes from low to high on switch
activation. Switch output 76 is a two-terminal output that presents low
or high impedance, the latter corresponding to switch activation. These
configurations are illustrative and exemplary, and any appropriate
configuration can be used. For example, the electronic circuit may
include a timing circuit that maintains a signal indicating switch
activation for a predetermined minimum time. In some example, noise
spikes may be excluded, for example by using an upper threshold level
above which the switch signal level is not expected to exceed during
normal switch activation, or by requiring a minimum predetermined time
over which the switch signal indicates switch activation.

[0059] In some examples, the electronic circuit is a computer circuit
including a microprocessor. The electronic circuit used for adjusting
thresholds may include a micro-processor used to adjust the thresholds
using software. For example, an algorithm can be used to determine an
adjusted threshold level using reference sensor signals collected over a
period of time.

[0060] FIG. 5 illustrates an illustrative method. Box 100 represents
measuring a reference capacitive signal. Box 102 represents adjusting the
threshold of one or more capacitive switches using the reference signal.
Box 104 represents determining the activation state of a capacitive
switch using the adjusted threshold.

[0061] The switch sensor and reference sensor may be of any conventional
or otherwise appropriate design. For example, a switch sensor may
comprise spaced apart conductive patches with a capacitive coupling to a
proximate finger or other body part, as known in the art. The conductive
patches may be coated with a thin dielectric layer, for example a plastic
layer, or other outer layer of a steering wheel.

[0062] A reference sensor may have a generally similar configuration to
the switch sensor. If there are differences in configuration between
reference and switch sensors, the appropriate threshold level for the
switch sensor may be appropriately determined by the electronic circuit,
taking these configuration differences into account.

[0063] Examples given above relate generally to capacitive sensors.
However, analogous configurations can be used for inductive, resistive,
optical, and other types of sensor. For example, an inductive switch may
comprise an inductive switch sensor providing an inductive switch signal,
an inductive reference sensor providing an inductive reference signal;
and an electronic circuit receiving the inductive switch signal and the
inductive reference signal, the electronic circuit determining switch
activation by comparing the inductive switch signal to a threshold signal
level, the threshold signal level being adjusted as a function of the
inductive reference signal. Analogous examples using resistive switches
and other switch technologies are possible. For example, resistive
reference sensors can be placed where e.g. a vehicle operator would make
skin contact during vehicle operation.

[0064] Examples also include improved methods of capacitive switch
operation for an electronic device. For example, a reference sensor may
be located within a power switch, other portion of the device that may be
touched to enable operation, or any portion of the device used for
holding the device. A reference signal is used to set the threshold level
for one or capacitive switches associated with the device. This may, for
example, allow improved use of electronic devices by gloved users. In
some examples, a reference sensor may be located within a first device,
and reference signals used to adjust capacitive switch thresholds for a
second device.

[0065] Capacitive switches may be used for a variety of purposes, such as
the control of a vehicle or any associated device, such as any vehicle
electronic system. Examples include capacitive switches used for climate
control adjustment, entertainment devices, navigation systems, and
vehicle operation. These examples are illustrative and not limiting to
the invention.

[0066] If no reference signal is obtained, the threshold may be set at a
default level. There may be a number of default levels corresponding to
various identified vehicle operators. In some examples, a reference
sensor may not be in wired electrical communication with switch sensor
and associated switch control electronics, and a reference signal (the
term as used herein includes a level thereof) may be wirelessly
communicated.

[0067] The invention is not restricted to the illustrative examples
described above. Examples described are not intended to limit the scope
of the invention. Changes therein, other combinations of elements, and
other uses will occur to those skilled in the art. The scope of the
invention is defined by the scope of the claims.